The present invention relates to an apparatus and a method for the recording of an image free of any line structure.
In displaying or recording an image, for example in television, transmission of photographs for the press, weather maps, written matter or the like through conductive lines, or by means of a radio frequency carrier, the image is at first scanned line-by-line and then reconstructed accordingly. Upon reconstruction or reproduction of the image, there is used a beam which is deflected line-by-line, and which is modulated in accordance with an image signal obtained during scanning of the original image. This method has been known for a long time, but has the disadvantage, that the line structure, which results from the Gaussian energy distribution of the beam used, and from the distance between the individual lines, becomes visible. These two facts, or causes, have so far permitted only a choice between two errors.
Adjacent lines are either spaced apart relative to the median width of the beam, which permits an optimal resolution of the image as a result of a good local separation of the image information, but the fluctuating intensity of successive lines due to an interspace occurring between adjacent lines is disturbing to an observer; if, on the other hand, the distance between the lines is smaller than the median width of the beam, and if the aforesaid brightness fluctuations can be eliminated by overlapping of lines, then the image resolution is diminished. These problems are known per se and are, for example, discussed in the Journal "Elektrotechnische Zeitschrift", volume 13, issue 22, of Oct. 30, 1961, page 590. In order to avoid these errors, the writing spot of the beam is either enlarged somewhat in a diffused manner, which results in a loss of resolution of the image, or the writing beam is rapidly wobbled in a direction transverse to the recording direction. This is indeed an improvement, and the resolution of the image is safeguarded, but successive lines still show remaining fluctuations in brightness, if the wobble amplitude cannot be tailored very exactly to the distance or spacing between adjacent lines. Furthermore, it is necessary to use deflection means and a video frequency controllable modulator, when using an electron beam as a recording beam, or when using a light beam; when using a modulator, additional light is being lost. As an acousto-optical modulator operates in a trouble-free manner only if the Bragg angle, through which the modulator is inclined with respect to the direction of the beam, can be maintained very accurately, a very precise adjustment of the modulator with respect to the light beam is required. Furthermore, any part of the beam, which has not been deflected must be removed, which causes further losses.
If the Bragg angle is not exactly adjusted, be it by the change of the wobble frequency or by a mechanical change during operation, then the intensity distribution in the direction of wobble changes, so that there occurs a higher beam intensity in one direction of deflection compared to the other direction. This causes, however, renewed visibility of lines.
From German Patent DT-OS No. 2,404,393 or the corresponding U.S. Pat. No. 3,876,829, there has become known another method to suppress the raster of an image. When using a light beam for recording, the light beam is subdivided by means of a plurality of adjacently positioned shutter-type openings into a plurality of partial beams, which are then recorded through optical means as a plurality of individual lines, so that an interspace between the lines is avoided. This method has the disadvantage, however, that light is being lost through the regions between the openings and peripheral regions. Additional light is being lost, as a light stop must be arranged in the center portion of the beam, which center portion is of approximately equal intensity, if the partial rays are also to have equal intensities. Additionally, the fabrication of such light stops is costly, and the light transmission characteristics of these light stops can be impaired, if they are contaminated by dust particles or the like.